Under certain climatic conditions, the rotor blades of wind turbines can ice up. This can lead to a reduction in the aerodynamic efficiency, to increased loading on the wind turbine by imbalances and to a hazard as a result of falling ice. Therefore, different rotor blade heating devices are known with which ice adhering to the rotor blades can be removed (de-icing) or icing up can already be counteracted before it occurs (anti-icing). Precise control of the rotor blade heating device is a significant factor in keeping the energy consumption of the rotor blade heating device low, avoiding overheating of the rotor blade and at the same time bringing about reliable de-icing or avoiding the formation of new ice.
The published European patent application EP 2 626 557 A1 discloses a method for controlling a rotor blade heating device in which the heat losses at the rotor blade are calculated taking into account the ambient temperature, the wind speed and the rotor rotational speed. The operation of the wind turbine is to take place in dependence upon the calculated heat losses. In particular, a rotor blade heating device is to be activated or the rotor rotational speed is to be reduced.
Another method for operating a wind turbine having a rotor blade heating device is disclosed in U.S. Pat. No. 7,182,575 B2. The method relates specifically to the situation in which the wind is calm or there is a very low wind speed. In this case, the generator of the wind turbine is to be used as a motor in order to operate the rotor at a low rotor rotational speed. At the same time, the pitch angle of the rotor blades is to be set in such a way that icing up on the leading edge on which a rotor blade heating device is arranged remains limited.
Another known possibility for controlling a rotor blade heating device uses a plurality of temperature sensors which are arranged on the rotor blade surface. These temperature sensors are used to measure a current temperature of the rotor blade. A rotor blade heating device is then activated and deactivated in dependence upon the measured temperature. In this way, it is possible to keep the rotor blade at a desired temperature. However, the high expenditure which the use of temperature sensors entails is disadvantageous. This applies to the installation of the temperature sensors and, in particular, to their maintenance and possibly necessary repair.